Improvement in construction of dental impression-molds



I same manner.

tnited mes intent dtiiiiirr.

WILLIAM CAMERON SMITH, OF WARRENSBURG, MISSOURI.

Letters Patent No. 105,008, elated July 5, 1,870.

The Schedule referred to in these Lejcters Patent and making part of the same pressions Aand'Oasts; vand do hereby declare that the' following is a full, clear, and exact description thereof, reference being had tothe accompanying drawings and to the letters of reference marked thereon.

The nature of my Ainvention consists iu putting the plaster in the mold in small quantities or thin layers, allowing each'layer to harden before the next one is put on, whereby the plaster vis allowed to expand in a vertical direction, instead of horizontally, thus avoiding the warping of the impression or cast.

In order to enable others skilled in the art to which my invention appertains to make and use the same, I will now proceed to describe the manner in which the same is or may be performed, referring to the annexed drawings, which, form a part of this speciication, and which represent a rear View of' an impression-cup containing an impression and cast.

M, represents the rear marginof the ordinary impression-cup, upon which is placed the bees-wax, H. This is made by vtaking a .bees-wax impression of the jaw, and afterward cutting away the wax to the depth of onefourth of an inch from its surface, to make room for thcvplaster with which theimpression of the mouth is taken, and which occupies the space marked by the letter L. The next space, designated by the letter R, is the Iirst layer of plaster composingr the cast, the plaster impression L having first been oiled, to` make them separate. Then a sufficient amount of prepared plaster is poured into the impression, and flowed over its entire surface to the depth of an eighth of an inch at the highest points, and one-fourth of an inch at the lower Ipoints. When the first laye-r becomes hard., a -second layer, Bis poured on iny the If the palatine arch is very high, still another thin'layer should 'be added before the 4last pouring, A, is made.

The object of my improvement is to prevent the warping of impression and cast caused by the expansion of the plaster in hardening.

In the ordinary process of taking animpression of the jaw, the plaster occupies the entire space between the. dividing-line between the impressionof the mouth and the cast, and the ordinaryimpression-eup in common use, except in cases where the palatine arch is very high.

A piecel of wax is placed in the center of the im pression-cup, to support thesoft plaster at that point against the roof of the mouth; but this has no reference to the eiiect produced by the expansion of the plaster, nor does it prevent the warping, but rather favors it.

The cause of warping of impressions in the ordinary process is the horizontal or lateral expansion of so thick a body of plaster being confined between the sidewalls of the impression-cup, causing the impression to bow up at or about' the center.v

In the ordinary process, the whole cast is Aformed atv one pouring. As the plaster hardens in so thick a body, it expands in horizontal direction, the lower margin or alveolar ridge being confined within the outer walls of the impression. The effect produced is to'warp the cast, so as to separate it from the impression at .or about the center, whereas, when the cast is Aconstructed by asuccession ot' thin,layers of plaster, made by applying the plaster in a batter suffi?` cient-ly thin 'to iow over the surface of the impression, by tipping it from side to side, until it begins to harden, forming a layer aboutr an eighth of an inch in thickness, more or less, a little thicker atthe lower points than elsewhere, and by continuing the process until the cast hasbecome of a proper thickness, the direction ofthe expansion will be so changedfas to prevent the possibility of warping.

vHaving thus fully described my invention, What I claim as new, and desire to secure by Letters Patent, is-

The dental cast, when formed of thin successive layers of plaster, substantially as described.

W. O. SMITH.

lVitnesses:

MYRON C. SIMKINS. A. C. Gme'es. 

